Article for Magnetic Heat Exchange and Method for Manufacturing an Article for Magnetic Heat Exchange

ABSTRACT

An article ( 1 ) for magnetic heat exchange extends in a first direction ( 3 ) and in a second direction ( 5 ) generally axially perpendicular to said first direction ( 3 ). The article ( 1 ) comprises at least one magnetocalorically active phase ( 2 ). The average thermal conductivity of the article ( 1 ) is anisotropic.

BACKGROUND

1. Field

Disclosed herein is an article for magnetic heat exchange and methodsfor manufacturing an article for magnetic heat exchange.

2. Description of Related Art

The magnetocaloric effect describes the adiabatic conversion of amagnetically induced entropy change to the evolution or absorption ofheat. By applying a magnetic field to a magnetocaloric material, anentropy change can be induced which results in the evolution orabsorption of heat. This effect can be harnessed to providerefrigeration and/or heating.

In recent years, materials such as La(Fe_(1-a)Si_(a))₁₃, Gd₅(Si, Ge)₄,Mn (As, Sb) and MnFe(P, As) have been developed which have a CurieTemperature, T_(c), at or near room temperature. The Curie Temperaturetranslates to the operating temperature of the material in a magneticheat exchange system. Consequently, these materials are suitable for usein applications such as building climate control, domestic andindustrial refrigerators and freezers as well as automotive climatecontrol.

Magnetic heat exchange technology has the advantage that magnetic heatexchangers are, in principle, more energy efficient than gascompression/expansion cycle systems. Furthermore, magnetic heatexchangers are environmentally friendly as chemicals such aschlorofluorocarbons (CFC) which are thought to contribute to thedepletion of ozone levels are not used.

Consequently, magnetic heat exchanger systems are being developed inorder to practically realise the advantages provided by the newlydeveloped magnetocaloric materials. Magnetic heat exchangers, such asthat disclosed in U.S. Pat. No. 6,676,772, typically include a pumpedrecirculation system, a heat exchange medium such as a fluid coolant, achamber packed with particles of a magnetic refrigerant working materialwhich displays the magnetocaloric effect and a means for applying amagnetic field to the chamber.

However, further improvements are desirable to enable a more extensiveapplication of magnetic heat exchange technology.

SUMMARY

Disclosed herein are embodiments of an article for magnetic heatexchange which can be reliably and cost effectively manufactured. Alsodisclosed herein are embodiments of methods by which the article may beproduced.

A particular embodiment relates to an article for magnetic heatexchange. The article extends in a first direction and in a seconddirection generally axially perpendicular to said first direction andcomprises at least one magnetocalorically active phase. The averagethermal conductivity of the article is anisotropic.

The article may be used as the magnetic refrigerant or magnetic workingmedium of a magnetic heat exchange system. Providing the article with ananisotropic average thermal conductivity has the advantage that heatgenerated within the article due to the magnetocaloric effect can beconducted to the surface of the article anisotropically. The heatexchange between the article and a cooling or heat exchange medium whichsurrounds the article may be anisotropic as well. As used herein, theterms “coolant” or “coolant medium” and “heat exchange medium,” are usedinterchangeably irrespective of whether the article is used to supplyheat to, or remove heat from, the heat exchange medium or working fluid.

The article may be arranged in the magnetic heat exchange system so thatthe most efficient thermal transfer occurs in directions perpendicularto the direction of coolant medium flow and so that the least efficientthermal transfer occurs in the direction of the coolant medium flow.This arrangement enables a more efficient heat exchange. Heat generatedby the magnetocaloric effect within the article can be conductedefficiently in directions perpendicular to the coolant medium flow tothe surface of the article where the heat is transferred to the coolantand carried by the coolant medium away from the article in the coolantflow direction.

The poorer thermal conductivity of the article in the direction of thecoolant flow hinders the transfer of the heat initially conducted awayfrom the article back into the article and in the opposite direction tothe coolant medium flow. Overall, the cooling efficiency of the articlefor magnetic heat exchange is improved by providing the article with ananisotropic average thermal conductivity.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments disclosed herein will now be explained with reference to theaccompanying drawings, which are intended to illustrate, but not limit,the scope of the appended claims.

FIG. 1 is a schematic diagram that illustrates a side view of anembodiment of an article for magnetic heat exchange,

FIG. 2 is a schematic diagram that illustrates a cross-sectional view ofthe article of FIG. 1,

FIG. 3 is a schematic diagram that illustrates a cross-sectional view ofan article for magnetic heat exchange having a microstructure accordingto a first embodiment disclosed herein,

FIG. 4 is a schematic diagram that illustrates a cross-sectional view ofan article for magnetic heat exchange having a microstructure accordingto a second embodiment disclosed herein,

FIG. 5 is a schematic diagram that illustrates a cross-sectional view ofan article for magnetic heat exchange having a microstructure accordingto a third embodiment disclosed herein,

FIG. 6 is a schematic diagram that illustrates a cross-sectional view ofan article for magnetic heat exchange having a microstructure accordingto a fourth embodiment disclosed herein, and

FIG. 7 is a schematic diagram that illustrates a cross-sectional view ofan article for magnetic heat exchange having a microstructure accordingto a fifth embodiment disclosed herein.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS

A magnetocalorically active material is defined herein as a materialwhich undergoes a change in entropy when it is subjected to a magneticfield. The entropy change may be the result of a change fromferromagnetic to paramagnetic behaviour, for example. Themagnetocalorically active material may exhibit, in only a part of atemperature region, an inflection point at which the sign of the secondderivative of magnetization with respect to an applied magnetic fieldchanges from positive to negative.

A magnetocalorically passive material is defined herein as a materialwhich exhibits no significant change in entropy when it is subjected toa magnetic field.

In an embodiment, the average thermal conductivity of the article in thefirst direction is less than the average thermal conductivity of thearticle in the second direction. In operation, the article is arrangedwith the first direction generally parallel to the coolant medium flowto produce the most efficient heat transfer.

In an embodiment, the article comprises a first length extending in saidfirst direction and a cross-sectional area extending in said seconddirection, the cross-sectional area having a second length. The averagethermal conductivity measured over the first length of the article isless than the average thermal conductivity measured over the secondlength of the article and, therefore, in the plane of thecross-sectional area. Again, in operation the first length of thearticle is arranged generally parallel and the second directiongenerally perpendicular to the flow direction of the coolant medium.

The anisotropy in the average thermal conductivity of the article can beprovided in a number of ways. For example, in some embodiments, thearticle further comprises a magnetocalorically passive phase having athermal conductivity which is greater than the thermal conductivity ofthe magnetocalorically active phase.

The anisotropic average thermal conductivity of the article may beproduced by various arrangements of the magnetocalorically active phaseand the magnetocalorically passive phase within the article. The thermalconductivity anisotropy may be produced at a microscopic level, (i.e.,by microscopic anisotropy), that is, the arrangement of the individualgrains or particles of the magnetocalorically passive phase and/ormagnetocalorically active phase which results in anisotropy in thermalconductivity. Alternatively, the thermal conductivity anisotropy may beproduced macroscopically, that is, due to arrangements of membersconsisting essentially of one of the magnetocalorically active andpassive phases.

In an embodiment, the magnetocalorically passive phase comprises aplurality of grains having, on average, a preferred orientation.Preferred orientation is used to describe an anisotropic arrangementand/or distribution of grains within the article. For example, even inembodiments where the individual grains may be generally spherical inshape and, therefore, individually have no preferred orientation.However, the spherical grains may be aligned in one or more rows or in amatrix of rows and columns and, therefore, have a preferred, i.e.physically anisotropic, arrangement within the article.

This anisotropic arrangement provides an article with an averageanisotropic thermal conductivity in the case that the thermalconductivity of the magnetocalorically passive phase is different fromthermal conductivity of the magnetocalorically active phase even if themagnetocalorically active phase is randomly arranged within the article.If the thermal conductivity of the magnetocalorically passive phase isgreater than the thermal conductivity of the magnetocalorically activephase, then the average thermal conductivity of the article in the longdirection of the row or in the plane of the matrix of the grains of themagnetocalorically passive phase is greater than that in directionsperpendicular to the long direction of the row or in the plane of thematrix of the grains of the magnetocalorically passive phase. Thearticle as a whole then has an anisotropic average thermal conductivity.

In an embodiment, the magnetocalorically passive phase comprises aplurality of grains, each having an elongate form with a long directionand at least one short direction generally perpendicular to the longdirection.

To produce thermal anisotropy at a microscopic level, the grains of themagnetocalorically passive phase may be arranged in the article with apreferred orientation and/or a preferred texture.

“Preferred orientation” is a term used to describe the physicalarrangement of the grains within the article. “Preferred texture” is aterm used to describe grains which are arranged within the article suchthat they have, on average, a preferred crystallographic orientation. Itis, therefore, possible that the grains have both a preferredorientation and a preferred texture.

In the case of grains having an elongate form arranged with a preferredtexture, the average thermal conductivity of the article in the longdirection of the grains is higher than the average thermal conductivityof the article in the short direction of the grains.

A thermally anisotropic article may be provided by arranging theplurality of elongate grains of the magnetocalorically passive phase inthe article so that on average their long direction extends generallyperpendicular to the first direction of the article. The plurality ofelongate grains of the magnetocalorically passive phase may be arrangedin the article so that on average their short direction extendsgenerally parallel to the first direction of the article. Thesearrangements provide an article with an average thermal conductivitywhich is higher in directions perpendicular to the first direction andlower in directions parallel to the first direction.

In operation, the article is arranged so that the long direction of thegrains is orientated generally perpendicular to the coolant medium flowdirection and the short direction of the grains is orientated generallyparallel to the coolant medium flow. This arrangement discourages heatflow through the article in directions opposite to the coolant mediumflow.

In an embodiment, the magnetocalorically active phase comprises aplurality of grains arranged in the article with, on average, apreferred orientation. In this case, the term “preferred orientation” isagain used to denote an anisotropic arrangement of grains within thearticle.

In a further embodiment, the magnetocalorically active phase comprises aplurality of grains arranged in the article with a preferred textureand, in a further embodiment, also with a preferred orientation. In anembodiment, the magnetocalorically active phase comprises a plurality ofgrains, each having an elongate form with a long direction and at leastone short direction generally perpendicular to the long direction. Thegrains may be fibre-like or plate-like, for example.

To produce an article with thermal anisotropy at the microscopic level,the grains of the magnetocalorically active phase may be arranged in thearticle so that on average the long direction of the grains extendsgenerally perpendicular to the first length of the article. The grainsof the magnetocalorically active phase may also be arranged in thearticle so that on average the short direction of the grains extendsgenerally parallel to the first length of the article.

This arrangement provides an article with an average thermalconductivity which is higher in directions of the article parallel tothe long direction of the grains and with an average thermalconductivity which is lower in the short direction of the grains.

In some embodiments, both the magnetocalorically passive phase and themagnetocalorically active phase are arranged within the article with apreferred orientation and/or preferred texture. The grains of the twophases may be intimately mixed so as to provide thermal anisotropy at amicroscopic level.

In other embodiments, only the magnetocalorically active phase has apreferred orientation and/or texture or elongate grains to provide anarticle with an anisotropic average thermal conductivity. The articlemay comprise a magnetocalorically passive phase which has no preferredtexture. The magnetocalorically active phase may be distributed with apreferred orientation and/or texture among the grains of themagnetocalorically passive phase. Alternatively, the magnetocaloricallyactive phase may be distributed without a preferred orientation and/ortexture among grains of the magnetocalorically passive phase having apreferred orientation and/or texture. The magnetocalorically passivephase may provide a matrix in which the grains of the magnetocaloricallyactive phase are arranged. In such an embodiment, the article can bedescribed as a composite.

An article for magnetic heat exchange may also be provided with ananisotropic average thermal conductivity by arranging materials ofdifferent thermal conductivity at a macroscopic level. In an embodiment,the article comprises a plurality of first layers consisting essentiallyof the magnetocalorically active phase interleaved with a plurality ofsecond layers consisting essentially of the magnetocalorically passivephase.

In another embodiment, the article comprises only magnetocaloricallyactive phases and no substantial portion of magnetocalorically passivephases. In this sense, phase is used to denote a solid body and excludegases and air. The term “no substantial portion” is defined as less than10 vol %.

In this embodiment, an average anisotropic thermal conductivity isachieved by an anisotropic distribution of the density of the article.In particular, the density of the article varies macroscopically. Thisis provided in one embodiment by at least one first layer consistingessentially of a magnetocalorically active phase and having a firstdensity and at least one second layer consisting essentially of themagnetocalorically active phase and having a second density, the firstdensity being greater than the second density.

The first layer with the greater density has a greater thermalconductivity than the second layer with a lower density. Therefore, theaverage thermal conductivity of the article in directions perpendicularto the plane of the layers is lower than the average thermalconductivity of the article in directions parallel to the plane of thelayers. The article, therefore, has an anisotropic average thermalconductivity.

The density of the at least one first layer and the at least one secondlayer may be adjusted to the desired average value by controlling theporosity of the respective layer. The at least one first layer maycomprise a first average porosity and the at least one second layer maycomprise a second average porosity, the second average porosity isgreater than the first average porosity. This provides a first layerwith a greater density than the second layer and an article with ananisotropic average thermal conductivity.

In a further embodiment, the at least one first layer and the at leastone second layer are arranged in a stack, wherein adjacent layers are inphysical contact with one another. The adjacent layers may be connectedto their immediate neighbour by a layer of an adhesive material or bedirectly connected to each other by sintering of material of theadjacent layers, for example.

The first layers and the second layers have a thickness which extendsgenerally parallel to the first direction of the article and a plane ofa lateral area extending generally in the second direction of thearticle (e.g., perpendicularly to the first direction of the article).Each layer is built up from a plurality of layers of grains or particlesof the respective phase.

In operation, the article is arranged so that the cross-sectional orlateral area of the layers extends in a planar fashion in directionsthat are generally perpendicular to the coolant flow direction and thethickness of the layers extends generally parallel to the coolant flowdirection. The thermal conductivity of the magnetocalorically passivephase is, preferably, greater than the thermal conductivity of themagnetocalorically active phase in this arrangement of the article inorder that the average thermal conductivity of the article in thecoolant flow direction is less than the average thermal conductivity ofthe article in directions perpendicular to the coolant flow direction.

In another embodiment, the article comprises a plurality of activelayers, each active layer comprising a magnetocalorically activematerial having a T_(c) which is different from the T_(c) of themagnetocalorically active material in an adjacent layer. In a furtherembodiment, the magnetocalorically active material of each of the layersis selected, along with the order in which the materials are arranged,in order that the T_(c) progressively increases from one end of thearticle to the other.

The use of articles comprising a plurality of magnetocalorically activematerials having different T_(c)'s, has the advantage that the operatingrange of the heat exchanger in which the article is used is increased.The Curie temperature T_(c) translates to the operating temperature and,since a range of T_(c)'s are provided, the operating range of the heatexchanger is increased. This enables the heat exchanger to providecooling and/or heating over a wider operating temperature range and toprovide cooling and/heating from a starting temperature to asmaller/larger lowermost/uppermost temperature, respectively, than thatpossible using magnetocalorically active material having a single T_(c).

In a further embodiment, the article further comprises at least onethermal barrier comprising a thermal conductivity which is less than thethermal conductivity of the magnetocalorically active phase.

The thermal barrier hinders thermal transfer from the region of thearticle on one side to the region of the article on the other side ofthe thermal barrier. The thermal barrier can be arranged so that thermaltransfer in the direction of the coolant medium flow is hindered, thusfurther improving the efficiency of the magnetic heat exchange.

In a further embodiment, the article comprises a plurality of thermalbarriers arranged at intervals along the first direction of the article.If a plurality of portions with differing T, are provided, the thermalbarrier may be arranged between adjacent portions.

The magnetocalorically active phase may be one or more of Gd, aLa(Fe_(1-b)Si_(b))₁₃-based phase, a Gd₅(Si, Ge)₄-based phase, a Mn(As,Sb)-based phase, a MnFe(P, As)-based phase, a Tb—Gd-based phase, a (La,Ca, Pr, Nd, Sr)MnO₂-based phase, a Co—Mn—(Si, Ge)-based phase and aPr₂(Fe, Co)₁₇-based phase. These basic compositions may further comprisefurther chemical elements which may substitute partially or in full forthe listed elements. These phases may also comprise elements which areaccommodated at least in part interstitially within the crystalstructure, for example, hydrogen. These phases may also include impurityelements and small amounts of elements such as oxygen.

In a further embodiment, the grains of the magnetocalorically activephase comprise a corrosion protection coating. This corrosion protectioncoating may comprise one or more metals, alloy, polymers, ceramics orinorganic compounds. The metal may be Al, Cu or Sn and the alloy maycomprise one or more of Al, Cu and Sn. An inorganic corrosion protectioncoating may be provided by a phosphate, for example a zinc phosphate.The corrosion protection coating may be applied to increase the workinglife of the magnetocalorically active phase since the corrosion anddegradation of the magnetocalorically active material intonon-magnetocalorically active phases is at least slowed, or evenprevented entirely, over the working lifetime of the magnetocaloricallyactive material, due to the corrosion protection coating.

The article may further comprise an effective porosity. The term“effective porosity” is used herein to describe a porosity of thearticle which has a measurable effect on the efficiency of the magneticheat exchange.

The effective porosity comprises at least one channel within the body ofthe article which extends from a first side of the article to a secondside of the article. The porosity may be in the range of 10 vol. % to 60vol. % based upon the total volume of the article.

The effective porosity may be provided in the form of a series ofinterconnected channels in flow communication with each other forming ahollow network of skeleton type structure within the body of thearticle. The heat exchange fluid or coolant can then flow through thehollow network from one side of the article to the other.

The effective porosity may be provided by loosely compacting the powderfrom which the article or a portion thereof is formed, or by looselycompacting the powder followed by sintering, to form in each case a bodywith a density of less than 100% such that the unoccupied volumeprovides an interconnected hollow network though which the heat exchangemedium can flow.

These embodiments of a article having an effective porosity have theadditional advantage that the surface area of the article is increased.The coolant is in contact with inner surfaces, that is the surfaces ofthe interconnected channels that provide the effective porosity, andwhich are positioned within the body of the article, as well as with theoverall outer surface of the article. Thus, the contact area between thearticle and the heat exchange fluid is increased. Consequently, theefficiency of the magnetic heat exchange may be further increased.

The article may further comprise at least one channel different from theinterconnected channels that provide effective porosity. The channel maybe provided in the form of a through-hole which is surrounded by thearticle or may be provided in the form of a channel in an outer surfaceof the article. One or more channels have the advantage of increasingthe surface area of the article which can further improve the heatexchange efficiency between the article and the coolant. The channel maybe formed by extrusion or profile rolling, for example.

In a further embodiment, the channel can be adapted to direct the flowof the coolant. The position of the channel is determined by the designof the heat exchange system in which the article is to operate. Thechannel may be adapted to direct the flow of the coolant with reducedor, optimally, minimum turbulence in order to increase the efficiency ofthe heat exchange.

The article may be a component of a heat exchanger, a cooling system, anair conditioning unit for a building or a vehicle, in particular anautomobile, or a climate control device for a building or an automobile.The climate control device may be used as a heater in winter and as acooler in summer by reversing the direction of the fluid coolant or heatexchanger medium. This is particularly advantageous for automobiles andother vehicles as the space available within the chassis foraccommodating the climate control system is limited by the design of thevehicle.

The article may also comprise an outer protective coating. The outerprotective coating may comprise a metal, an alloy or a polymer. Thematerial of the outer protective coating may be chosen so as to bechemically, as well as mechanically, stable during the lifetimeoperation of the article in the heat exchange medium. If the coating isapplied to the finished article, it is not subjected to highertemperatures, for example during sintering, or working of the article.In this case, a polymer with a relatively low decomposition temperatureor melting temperature may be used.

The heat exchange medium or working fluid used to exchange heat with thearticle may comprise ethanol or glycol, mixtures of water, ethanol orglycol or an alternative material with a high thermal conductivity inorder to increase the efficiency of the heat exchange between the heatexchange medium and the article. In some circumstances, the heatexchange medium may be corrosive to the magnetocalorically activematerial and/or the magnetocalorically passive material of the matrix.Therefore, an additional outer protective coating may be used to provideadditional protection.

The article according to one of these embodiments may be used as acomponent of a heat exchanger, a refrigeration system, a climate controldevice, an air-conditioning unit, or an industrial, commercial ordomestic freezer. The article is arranged so that the first direction ofthe article is arranged generally parallel to the direction of heat flowduring operation.

The invention also provides methods of manufacturing an article formagnetic heat exchange. In an embodiment, a magnetocalorically activephase is provided and a magnetocalorically passive phase comprising aplurality of particles are provided. The magnetocalorically active phaseand the magnetocalorically passive phase are assembled and compacted toform an article. A preferred orientation, that is, a preferred physicalarrangement, of at least a plurality of grains of the magnetocaloricallypassive phase, on average, is produced.

In an embodiment, a precursor of a magnetocalorically active phase isprovided and a magnetocalorically passive phase comprising a pluralityof particles are provided. The precursor of the magnetocaloricallyactive phase and the magnetocaloritally passive phase are assembled andcompacted to form an article. A preferred orientation of the pluralityof grains of the magnetocalorically passive phase is produced. In thisembodiment, the article is reaction sintered, wherein themagnetocalorically active phase forms from the precursor.

The article is provided with an anisotropic thermal conductivity due tothe preferred orientation of the magnetocalorically passive phase sincethe thermal conductivity of the plurality of grains of themagnetocalorically passive phase is higher in the longer direction ofthe grains than in the shorter direction. As previously discussed, thegrains may also have, on average, a preferred texture ofcrystallographic orientation.

The preferred orientation may be produced at least in part by thecompaction process or may be produced in part or entirely in a separatemethod step which may take place before or after compaction.

In an embodiment, the compaction is carried out so as to inducepreferred orientation of at least the grains of the magnetocaloricallypassive phase and/or at least the grains of the magnetocaloricallyactive phase

In an embodiment, the average preferred orientation of at least theplurality of grains of the magnetocalorically passive phase is producedat least in part by applying a magnetic field. This method may be usedwhen the magnetocalorically passive phase is ferromagnetic, for example,comprises Fe or FeSi.

A magnetic field may also be used to provide a preferred orientation ofparticles of the magnetocalorically active phase if themagnetocalorically active phase is in the ferromagnetic state. If themagnetocalorically active phase is ferromagnetic at temperatures belowits Curie Temperature, the magnetic field may be applied at atemperature below the Curie temperature of the magnetocalorically activephase in order to magnetically align the particles so that at least someof the particles have the preferred orientation.

The magnetic field may be applied before the compaction is carried outso as to provide a preferred orientation of the particles of themagnetocalorically passive phase and/or magnetocalorically active phase.This preferred orientation is maintained during compaction and in thecompacted article.

The compaction may be carried out so as to induce a preferred texture inat least the magnetocalorically passive phase. If the particles of themagnetocalorically passive phase have anisotropic dimensions, thecompaction may be carried out by arranging the compaction direction sothat it is generally perpendicular to the long direction of the grains,or, in the case of plate-like grains, generally perpendicular to theplane of the plate. A degree of preferred orientation may also beprovided by shaking the powder in directions perpendicular to thecompaction direction before the compaction is carried out. Thisencourages plate-like grains to take on a stratified structure beforecompaction.

The compaction is carried out so that the grains of themagnetocalorically passive phase are on average orientated with theirlong direction perpendicular to the first direction of the article. Thisproduces an article with a higher average thermal conductivity indirections perpendicular to the first direction and a lower averagethermal conductivity in the first direction.

In an embodiment, the average preferred orientation of at least theplurality of grains of the magnetocalorically passive phase and/or ofthe magnetocalorically active phase is produced at least in part bymechanical deformation of the article after the compaction. Themechanical deformation may be carried out by one of more of rolling,swaging, drawing and extruding.

In an embodiment, the magnetocalorically active phase and themagnetocalorically passive phase are assembled by intimately mixing themagnetocalorically active phase and the magnetocalorically passive phasewith one another. This method produces an article with an anisotropicthermal conductivity produced on a microscopic scale.

In a further embodiment, the magnetocalorically active phase and themagnetocalorically passive phase are assembled by alternately arranginglayers consisting essentially of the magnetocalorically active phaseinterleaved with layers consisting essentially of the magnetocaloricallypassive phase. This method produces an article with an anisotropicaverage thermal conductivity on a macroscopic scale.

In an embodiment, additionally one or more of a lubricant, an organicbinder and a dispersant are added to the assembled magnetocaloricallyactive phase and magnetocalorically passive phase. These additives canhelp to increase the density of the article.

The assembled magnetocalorically active phase and magnetocaloricallypassive phase may be compacted by one or more of rolling and pressing.Rolling may be used to produced a long length article in which thethermal conductivity in directions along the length of the article andacross its breadth is greater than the thermal conductivity in adirection across its thickness. Such articles can be arranged in alaminated stack. Pressing may be used to produce an article in which thethermal conductivity is greater across the breadth of the article thanalong its length as the long direction of the magnetocalorically passivephase are orientated generally perpendicularly to the length of thearticle.

In a further embodiment, the article is heated during compaction. A heattreatment may be used to further compact the article as well as sinterthe grains together. If precursor is used, the heat treatment is carriedout under conditions selected so that the magnetocalorically activephase is formed from the precursor.

A heat treatment during compaction may also be used to further increasethe degree of texture of the grains due to reorientation of the grainsas well as grain growth in a preferred direction, advantageously thelong direction of the grains.

In a further embodiment, a magnetic field is applied during compactionso as to magnetically orientate the grains of the magnetocaloricallypassive phase and/or active phase so that on average their longdirection is oriented generally perpendicular to the first direction ofthe article. Heat may also be applied at the same time. This method maybe used when the magnetocalorically passive phase comprises a softmagnetic material such as Fe or FeSi or when the magnetocaloricallyactive phase has already formed and is ferromagnetic during the pressingprocess.

A method of manufacturing an article without a magnetocaloricallypassive phase and with an average anisotropic thermal conductivity isalso provided. In this method, at least one first plate consistingessentially of a magnetocalorically active phase and having a firstdensity and at least one second plate consisting essentially of amagnetocalorically active phase and having a second density is provided.The first density of the first plate is greater than the second densityof the second plate. The first plate and the second plate are arrangedin a stack to provide an article for magnetic heat exchange.

The first and the second plates have differing average thermalconductivities due to their differing densities. A higher densityprovides a higher average thermal conductivity. Therefore the averagethermal conductivity in the stack direction, that is perpendicular tothe plane of the plates is lower than the average thermal conductivityin the plane of the plates.

In an embodiment, the first plate and the second plate are arranged sothat they are in physical contact with one another.

In a further embodiment, the first plate comprises a first porosity andthe second plate comprises a second porosity, the second porosity beinggreater than the first porosity. This provides a first plate with agreater density than the second plate.

The first plate and/or the second plate may be produced by compactingparticles of a magnetocalorically active phase or precursor of amagnetocalorically active phase.

The conditions of the compaction are adjusted so as to produce a lowerporosity in the first plate than in the second plate. For example, thecompaction pressure and, if used, temperature, can be increased to lowerthe porosity and increase the density of the plate. Conversely, thecompaction pressure and, if used, temperature, can be decreased toincrease the porosity and decrease the density of the plate.

In a further embodiment, a plurality of first plates and a plurality ofsecond plates are provided. The plurality of first plates and theplurality of second plates are interleaved with one another in astacking direction of the article. The article produced has amulti-layer or stratified structure.

In a particular embodiment, after the article is compacted or after thearticle has been produced, an outer protective coating may be applied tothe article. The outer protective coating may be for example, applied bydipping, spraying or electro-deposition.

FIG. 1 illustrates a side view of an article 1 for magnetic heatexchange which comprises a magnetocalorically active phase 2 which, inthis particular embodiment, consists essentially of aLa(Fe_(1-a-b)Co_(a)Si_(b))₁₃-based phase with a Curie Temperature,T_(c), of 20° C. The article 1 provides the magnetic refrigerant workingcomponent of a non-illustrated magnetic heat exchange system whichfurther includes a pumped recirculation system, a heat exchange medium,such as a fluid coolant, and means for applying a magnetic field to thechamber.

The article 1 has a first length 1 and a second length b extendinggenerally perpendicularly to the first length 1. The direction of thecoolant flow is indicated in FIG. 1 by the arrows 3. Depending onwhether the heat exchange system is used to provide refrigeration or toprovide heating, the coolant may flow in two opposing directions. Inoperation, the first length 1 of the article 1 is arranged so that itextends in the coolant flow direction 3 and the second length b isarranged so that it extends generally perpendicularly to the coolantflow direction 3. In the view illustrated in FIG. 1, the coolantdirection is from top to bottom. The article 1 is also provided with aplurality of channels 4 in its outer surface which extend in thedirection of the coolant flow 3 and increase the surface area of thearticle 1 so as to improve the effectiveness of the heat transfer fromthe article 1 to the coolant.

According to the invention, the article 1 has an anisotropic averagethermal conductivity. In particular, the average thermal conductivity ofthe article in the direction of the coolant flow 3 is lower than theaverage thermal conductivity of the article 1 in directionsperpendicular to the coolant flow 3, indicated by the arrows 5, in whichthe second length b of the article 1 extends.

This arrangement enables the magnetically induced heat produced by themagnetocalorically active phase 2 within the article 1 to be conductedefficiently to the outer surfaces 6 of the article 1 in the direction ofthe arrows 5 and from there to the coolant while at the same timepreventing conduction of the magnetically induced heat within thearticle in directions opposing the coolant flow direction 3. Thisprevents a type of internal short circuit within the article 1 in whichheat carried from the cold end 7 to the hot end 8 by the coolant issimply conducted back to the cold end 7 by the article 1 itself.

FIG. 2 illustrates a cross-sectional view of the article 1 of FIG. 1.The cross-sectional view of FIG. 2 illustrates that the article 1 has alayered structure and comprises three active portions 9, 10, 11, eachcomprising a magnetocalorically active phase 2. Each of the three activeportions 9, 10, 11 comprises a magnetocalorically active phase having adifferent T_(c) such that the T_(c) of each active portion increases inthe direction of coolant flow 3. Each active portion 9, 10, 11 isseparated from its neighbour by a thermal barrier 12 which furtherprevents thermal conductivity between adjacent portions 9, 10, 11 of thearticle 1.

Each portion 9, 10, 11 further comprises a magnetocalorically passivephase 13 which has a greater thermal conductivity than the thermalconductivity of the magnetocalorically active phase 2. The anisotropicaverage thermal conductivity of the article 1 is provided by providingthe grains 14 of the magnetocalorically passive phase 13 in a layeredtype arrangement. The layered arrangement may be providedmicroscopically, as illustrated in FIGS. 3 and 5, or macroscopically, asillustrated in FIGS. 2 and 4. Arrangements including a combination ofboth microscopic and microscopic layering may also be used.

In the embodiment illustrated in FIG. 3, the magnetocalorically passivephase 13 comprises a plurality of grains 14 having a general plate-likeform and for illustrative purposes only illustrated in the drawing asblack shaded, filled rectangular plates. The plate-like grains 14 have along direction 15 and a short direction 16 which is arranged generallyperpendicularly to the long direction 15. The plate-like grains 14 arearranged within the article 1 such that on average the long direction 15extends in directions parallel to the second length b of the article 1and generally perpendicular to the coolant flow direction 3. The shortdirection 16 of the grains 14 extends on average generally parallel tothe first length 1 of the article and parallel to the coolant flowdirection 3.

The plurality of grains 14 of the magnetocalorically passive phase 13are arranged within the article such that they have a preferredorientation and/or preferred texture. Preferred orientation is used todenote the physical arrangement of the grains and preferred texture isused to denote the crystallographic orientation of the grains. Due tothis preferred orientation and/or texture, the average thermalconductivity of the article 1 in directions perpendicular to the coolantflow direction 3 is higher than the average thermal conductivity of thearticle 1 in directions parallel to the coolant flow direction 3.

The grains 17 of the magnetocalorically active phase 2 are, in thisembodiment, generally isotropic in comparison to the grains 14 of themagnetocalorically passive phase 13 and for illustrative purposes onlyare illustrated in the drawing as open, white areas of variable outline.The grains 17 of the magnetocalorically active phase 2 are illustratedin FIG. 3 as distributed among the grains 14 of the magnetocaloricallypassive phase 13 and forming a matrix therefore. Alternatively, themagnetocalorically passive phase 13 may provide the matrix of thearticle 1 and act as a binder for the grains 17 of themagnetocalorically active phase 2. The embodiment illustrated in FIG. 3provides an article 1 comprising anisotropic average thermalconductivity due to the distribution of the grains 14 of themagnetocalorically passive phase 13 on the microscopic scale.

In the second embodiment illustrated in FIG. 4, the grains 14 of themagnetocalorically passive phase 13 also have a generally plate-likeform. The grains 14 are also arranged in the article 1 with a preferredorientation such that their long direction 15 extends in directionsgenerally parallel to the second length b of the article 1 and indirections generally perpendicular to the coolant flow direction 3.

In the second embodiment of FIG. 4, as in the embodiment of FIG. 2, theanisotropic thermal conductivity of the article 1 is provided by alayered structure in which layers 18 consisting essentially of amagnetocalorically active phase 2 are interleaved with layers 19consisting essentially of a magnetocalorically passive phase 13. In theembodiment illustrated in FIG. 4, the anisotropic average thermalconductivity of the article 1 is provided macroscopically.

A single layer 19 of a magnetocalorically passive phase 13 sandwichedbetween two layers 18 of magnetocalorically active phase 2 areillustrated in FIG. 4, although any number of layers can be provided.The stacked arrangement of layers 18, 19 is built up in the direction ofthe first length 1 of the article 1.

The magnetocalorically passive phase 13 may be a metal and in someembodiments, is magnetic. A magnetic magnetocalorically passive phase 13has the advantage that the grains 14 can be aligned magnetically toproduce the preferred orientation.

The article 1 may also comprise an outer coating 20 in order to protectthe article 1 and, in particular, the magnetocalorically active phase 2,from corrosion by the environment and, in particular, by the coolant.

The article 1 of FIG. 3 may be fabricated by intimately mixing a powderof a magnetocalorically active phase 2 and a powder of amagnetocalorically passive phase 13 and compacting the resultingmixture. The preferred orientation of the grains 14 of themagnetocalorically passive phase 13 may occur at least partly as aresult of settling of the powder in the mould in which the powdermixture is compacted. The preferred orientation of the grains 14 mayalso be induced by the compaction process. The direction of pressureexerted during the compaction process is generally perpendicular to thelong direction 16 of the plate-like grains 14 so that the plate-likegrains 14 are encouraged to lie with their long direction perpendicularto the direction of compaction. Furthermore, the plate-like grains 14may slide over one another so increasing the degree of preferredorientation.

The degree of preferred orientation and/or texture may also be increasedby applying heat during the compaction process. The heat may encouragesintering of the grains which, given a preferred growth direction, canfurther increase the anisotropy of the plate-like grains and the degreeof preferred orientation.

The preferred orientation of the grains may also be at least in partproduced by alignment processes which take place before or aftercompaction. The preferred orientation may also be achieved substantiallyseparate from the compaction process.

In a further embodiment, the magnetocalorically passive phase may beprovided by a magnetic material and a magnetic field applied so as toinduce preferred orientation in the desired direction within the article1. The magnetic field may be applied before and/or during compaction.Furthermore, a heat treatment may also be applied at the same time asthe magnetic field.

The article 1 may also be fabricated by reaction sintering. In thisembodiment, precursor of the magnetocalorically active phase isprovided. The precursor consists of non-magnetocalorically active phasesin amounts to produce the magnetocalorically active phase when theyreact with one another. The precursor may be intimately mixed with themagnetocalorically passive phase to produce an anisotropically thermallyconductive article at a microscopic scale. The precursor of themagnetocalorically active phase may also be provided as a discreet layeror layers within a macroscopically layered arrangement similar to thatillustrated in FIG. 4. After or during compaction, the article is heatedso as to reaction sinter the precursor and form the magnetocaloricallyactive phase.

The preferred orientation of the magnetocalorically passive phase mayalso be achieved by other methods known in the art. For example, themagnetocalorically passive phase could be subjected to a rollingtreatment or may be provided as a thin layer with a preferredorientation.

If an outer coating is provided, the coating may be applied to thearticle after compaction and any heat treatment process. The coating maybe applied by e.g., dipping, spraying or electroplating.

In a further embodiment, illustrated in FIG. 5, the magnetocaloricallyactive phase 2 also comprises grains 21 having an elongate form. Forillustrative purposes only, the grains 21 of the magnetocaloricallyactive phase 2 are shaded black and the grains 14 of themagnetocalorically passive phase 13 are left unshaded. In thisembodiment, the magnetocalorically active phase 2 is also arranged inthe article 1 with a preferred orientation such that the long direction22 of the grains 21 extends in directions generally perpendicular to thecoolant flow direction 3 and the short direction 23 of the grains 21extends in the direction of the coolant flow 3.

FIG. 6 illustrates an embodiment of an article 1 for use as the workingcomponent of a magnetic heat exchange system according to a fourthembodiment.

The article 1 of the fourth embodiment comprises a plurality of grains17 of a magnetocalorically active phase 2 and a plurality of grains 14of a magnetocalorically passive phase 13. For illustrative purposesonly, the grains 17 are unshaded and the grains 14 are shaded black. Onaverage, each of the grains 14 and/or 17 has a shape which is generallyisotropic (e.g., generally spherical). In this embodiment, the article 1has anisotropic thermal conductivity due to the preferred orientation ofthe isotropically-shaped grains 14 of the magnetocalorically passivephase 13.

The generally spherical grains 14 of the magnetocalorically passivephase 13 comprises a ferromagnetic material, in this case iron. Thegrains 14 are arranged in a plurality of rows or chains 24 having a longdirection which extends in directions generally parallel to the seconddirection 5 and perpendicular to the coolant flow direction 3 of thearticle 1. The chains 24 are arranged in a series of layers arranged oneabove the other in the stack direction 28 which is parallel to thecoolant flow direction 3. The grains 17 of the magnetocalorically activephase 2 are arranged between the chains 24 of the magnetocaloricallypassive phase 13 and also have a degree of preferred orientation. Thepreferred orientation of the magnetocalorically active phase 2 isproduced as a result of the pre-formation of a preferred orientation inthe magnetocalorically passive phase 13.

The thermal conductivity of the magnetocalorically passive phase 13 isgreater than the thermal conductivity of the magnetocalorically activephase 2. The article 1, therefore, has on average an anisotropic thermalconductivity. In particular, the thermal conductivity of the article 1is greater in the second direction 5 than in the coolant flow direction3.

The article 1 of the fourth embodiment illustrated in FIG. 6 isfabricated by intimately mixing particles of the magnetocaloricallyactive phase 2 and particles of the magnetocalorically passive phase 13and placing these in a compaction vessel such as a die. A magnetic fieldis applied in the second direction 5 which causes the ferromagneticparticles of the magnetocalorically passive phase 13 to align themselvesin the direction of the applied magnetic field to create the pluralityof chains 24.

The preferred orientation of the grains 17 of the magnetocaloricallyactive phase 2 occurs due to the restriction of the movement of theparticles of the magnetocalorically active phase 2 within the article 1due to the pre-formation of the aligned chains 24 of the particles ofthe magnetocalorically passive phase 13.

In a further embodiment, the magnetocalorically active phase 2 isferromagnetic at temperatures below its Curie temperature. Therefore, ifthe magnetic field is applied to the powder mixture at temperaturesbelow the Curie temperature of the magnetocalorically active phase 2, apreferred orientation of the particles of the magnetocalorically activephase 2 in the direction of the applied magnetic field can also beachieved.

FIG. 7 illustrates an article 1′ for use as the working component of amagnetic heat exchange system according to a fifth embodiment.

The article 1′ of the fifth embodiment consists essentially of one ormore magnetocalorically active phases 2. For purposes of illustration,these phases are depicted as unshaded areas. The article 1′ of the fifthembodiment is free from magnetocalorically passive phases. Theanisotropic average thermal conductivity of the article 1′ is provided,in this embodiment, by an anisotropic distribution of the density of thearticle 1′ and, in particular, and anisotropic distribution of theporosity of the article 1′.

The article 1′ of the fifth embodiment includes a plurality of layers ofwhich five are illustrated in FIG. 7. Three first layers 25 have arelatively low porosity and two second layers 26, which are arrangedbetween adjacent first layers 25, include a higher degree of porositythan that of the first layers 25. In the illustration of FIG. 7, thepores 27 are indicated by the black shaded regions.

The pores have a lower thermal conductivity than the magnetocaloricallyactive phase 2. Therefore, the second layers 26 have a lower averagethermal conductivity than the first layers 25. This provides an article1′ with an average thermal conductivity measured from end to end of thearticle in the coolant flow direction 3 which is less than the averagethermal conductivity measured from the side face to side face of thearticle 1′ in the second direction 5.

The multilayer or laminated article 1′ of the fifth embodiment may befabricated by stacking a plurality of layers of differing densities orporosities together. In particular, layers 25 having a higher densityare interleaved with layers 26 having a lower density. The layers 25, 26are stacked directly on top of one another in the stack direction 28 sothat each layer is in physical contact with its immediate neighboringlayer. The layers 25, 26 may be fixedly attached to their neighbour byan adhesive.

The article 1′ of the fifth embodiment may be fabricated by firstfabricating a plurality of first layers 25 in the form of plates orfoils having a first density. A plurality of second layers 26 in theform of plates or foils may be fabricated having a second density whichis lower than the first density.

The first layers 25 and second layers 26 are stacked alternately on topof one another joining each layer 25, 26 to the underlying one toproduce article 1′.

The plates or foils which form layers 25, 26 may be fabricated bycompacting particles of a magnetocalorically active phase which thenform grains of magnetocalorically active phase 2. The density of theplates and foils can be adjusted by adjusting the compaction conditions.For example, the compaction pressure and, if a heat treatment is used,the temperature and time of the heat treatment may be increased toachieve a higher density in the plate or foil.

The article 1′ of the fifth embodiment may also further comprise anouter protective coating, thermal barrier layers, a corrosion protectioncoating covering the grains of the magnetocalorically active phase asdescribed in connection with the previous embodiments.

The invention having been described with reference to certain specificembodiments, it will be understood that these specific embodiments areprovided in order to illustrate, and not limit, the scope of theappended claims.

1. An article for magnetic heat exchange, the comprising: at least onemagnetocalorically active phase, wherein the article extends in a firstdirection and in a second direction generally perpendicular to the firstdirection, and wherein the average thermal conductivity of the articleis anisotropic such that the average thermal conductivity in the firstdirection differs from the average thermal conductivity in the seconddirection.
 2. The article according to claim 1, wherein the averagethermal conductivity in the first direction is less than the averagethermal conductivity of the article in the second direction.
 3. Thearticle according to claim 1 wherein the first direction corresponds tothe thickness of the article, and the second direction corresponds to adirection in a plane of a lateral area extending generally perpendicularto the first direction, and wherein the average thermal conductivitymeasured over the thickness of the article is less than the averagethermal conductivity measured in a direction in the plane of a lateralarea of the article.
 4. The article according to claim 1, furthercomprising: a magnetocalorically passive phase having a thermalconductivity which is greater than a thermal conductivity of themagnetocalorically active phase.
 5. The article according to claim 4,wherein the magnetocalorically passive phase comprises a plurality ofgrains having, on average, a preferred orientation.
 6. The articleaccording to claim 5, wherein the plurality of grains of themagnetocalorically passive phase comprise an elongate form having a longdirection, and a short direction generally perpendicular to the longdirection.
 7. The article according to claim 5, wherein at least some ofthe plurality of grains of the magnetocalorically passive phase arearranged in the article with a preferred texture.
 8. The articleaccording to claim 6, wherein the plurality of grains of themagnetocalorically passive phase are arranged in the article so that onaverage their long direction extends generally perpendicular to thefirst direction of the article.
 9. The article according to claim 5,wherein the plurality of grains of the magnetocalorically passive phaseare arranged in the article so that on average their short directionextends generally parallel to the first direction of the article. 10.The article according to claim 1, wherein the magnetocalorically activephase comprises a plurality of grains arranged in the article with, onaverage, a preferred orientation.
 11. The article according to claim 10,wherein the plurality of grains of the magnetocalorically active phasehave, on average, a preferred texture.
 12. The article according toclaim 10, wherein the magnetocalorically active phase comprises aplurality of grains, each having an elongate form with a long directionand a short direction generally perpendicular to the long direction. 13.The article according to claim 12, wherein the grains of themagnetocalorically active phase are arranged in the article so that onaverage the long direction of the grains extends generally perpendicularto the first direction of the article.
 14. The article according toclaim 13, wherein the grains of the magnetocalorically active phase arearranged in the article so that on average the short direction of thegrains extends generally parallel to the first direction of the article.15. The article according to claim 10, wherein the grains of themagnetocalorically active phase comprise a corrosion protection coatingdisposed thereon.
 16. The article according to claim 15, wherein thecorrosion protection coating comprises a metal, an alloy, a polymer, aceramic, or an inorganic compound.
 17. The article according to claim15, wherein the corrosion protection coating comprises Al, Cu, Sn, or aphosphate.
 18. The article according to one claim 4, wherein themagnetocalorically active phase is disposed in a plurality of firstlayers interleaved with a plurality of second layers containing themagnetocalorically passive phase.
 19. The article according to claim 1,wherein the magnetocalorically active phase comprises at least one firstlayer having a first density, and at least one second layer having asecond density, wherein the first density is greater than the seconddensity.
 20. The article according to claim 19, wherein the at least onefirst layer has a first average porosity and the at least one secondlayer has a second average porosity, wherein the second average porosityis greater than the first average porosity.
 21. The article according toclaim 18, wherein the at least one first layer and the at least onesecond layer are arranged in a stack, wherein adjacent layers are inphysical contact with one another.
 22. The article according to claim18, wherein the first layers and the second layers each have a thicknessextending generally parallel to the first direction of the article and alateral area extending generally in the second direction of the article.23. The article according to claim 1, wherein the article comprises twoor more active portions arranged along the first direction, each portioncomprising a magnetocalorically active phase having a different Curietemperature T_(c).
 24. The article according to claim 23, wherein theT_(c) of the active portions increases in the first direction of thearticle.
 25. The article according to claim 1, further comprising: atleast one thermal barrier having a thermal conductivity which is lessthan the thermal conductivity of the magnetocalorically active phase.26. The article according to claim 25, wherein a plurality of thermalbarriers are arranged at intervals along the first direction of thearticle.
 27. The article according to claim 23, and further comprising athermal barrier having a thermal conductivity which is less than thethermal conductivity of the magnetocalorically active phase, that isarranged between adjacent active portions.
 28. The article according toclaim 1, wherein the magnetocalorically active phase comprises one ormore of Gd, a La(Fe_(1-b)Si_(b))₁₃-based phase, a Gd₅(Si, Ge)₄-basedphase, a Mn(As, Sb)-based phase, a MnFe(P, As)-based phase, aTb—Gd-based phase, a (La, Ca, Pr, Nd, Sr)MnO₃-based phase, a Co—Mn—(Si,Ge)-based phase and a Pr₂(Fe, Co)₁₇-based phase.
 29. The articleaccording to claim 4, wherein the magnetocalorically passive phasecomprises one or more of the elements, Al, Cu, Ti, Mg, Zn, Sn, Bi or Pb.30. The article according to claim 4, wherein the magnetocaloricallypassive phase comprises a soft magnetic material.
 31. The articleaccording to claim 30, wherein the soft magnetic material comprises oneor more of Fe, FeSi, Co, or Ni.
 32. The article according to claim 1,further comprising at least one channel in a surface of the article. 33.The article according to claim 32, wherein the channel is adapted todirect the flow of a heat exchange medium.
 34. The article according toclaim 1, further comprising an outer protective coating.
 35. The articleaccording to claim 34, wherein the outer protective coating comprises apolymer or a metal or an alloy.
 36. A heat exchanger, comprising thearticle according to claim
 1. 37. A refrigeration system, comprising theheat exchanger according to claim
 36. 38. An industrial, commercial, ordomestic freezer comprising the refrigeration system according to claim37.
 39. A method of manufacturing an article according to claim 4,comprising: providing a magnetocalorically active phase or a precursorof a magnetocalorically active phase, providing a magnetocaloricallypassive phase comprising a plurality of particles, assembling themagnetocalorically active phase or the precursor of a magnetocaloricallyactive phase and the magnetocalorically passive phase, compacting themagnetocalorically active phase or the precursor of a magnetocaloricallyactive phase and the magnetocalorically passive phase to form an articlehaving an average preferred orientation of at least the plurality ofgrains of the magnetocalorically passive phase in the article.
 40. Themethod according to claim 39, wherein the compacting comprises inducinga preferred orientation of at least the grains of the magnetocaloricallypassive phase.
 41. The method according to claim 39 wherein thecompacting comprises inducing a preferred orientation of at least thegrains of the magnetocalorically active phase.
 42. The method accordingto claim 39, wherein the average preferred orientation of at least theplurality of grains of the magnetocalorically passive phase or at leastthe plurality of grains of the magnetocalorically active phase, or both,is produced at least in part by applying a magnetic field to themagnetocalorically passive phase or to the magnetocalorically activephase or to both.
 43. The method according to claim 42, wherein themagnetic field is applied before the compacting.
 44. The methodaccording to claim 42, wherein the magnetic field is applied at atemperature less than the Curie Temperature of the magnetocaloricallyactive phase.
 45. The method according to claim 39, wherein theparticles of the magnetocalorically passive phase have on averageanisotropic dimensions and the compaction is carried out so that thegrains of the magnetocalorically passive phase are on average orientatedsuch that the grains have a long direction perpendicular to the firstdirection of the article.
 46. The method according to claim 39, whereinthe average preferred orientation of at least the plurality of grains ofthe magnetocalorically passive phase is produced at least in part bymechanical deforming the article after the compacting.
 47. The methodaccording to claim 46, wherein the mechanical deforming comprises one ofmore of rolling, swaging, drawing or extruding.
 48. The method accordingto claim 39 wherein the assembling of the magnetocalorically activephase and the magnetocalorically passive phase comprises intimatelymixing the magnetocalorically active phase and the magnetocaloricallypassive phase with one another.
 49. The method according to claim 39wherein the assembling of the magnetocalorically active phase and themagnetocalorically passive phase comprises alternately arranging layersconsisting essentially of the magnetocalorically active phase and layersconsisting essentially of the magnetocalorically passive phase.
 50. Themethod according to claim 39 wherein the compacting of themagnetocalorically active phase and the magnetocalorically passive phasecomprises rolling or pressing.
 51. The method according to claim 42,wherein the applying of the magnetic field during compactionmagnetically orientates the grains of the magnetocalorically passivephase so that on average the grains have a long direction that isoriented generally perpendicular to the first direction of the article.52. The method according to claim 42, wherein the applying of themagnetic field during compaction magnetically orientates the grains ofthe magnetocalorically active phase so that on average the grains have along direction that is oriented generally perpendicular to the firstdirection of the article.
 53. A method of manufacturing an article formagnetic heat exchange, comprising: providing at least one first plateconsisting essentially of a magnetocalorically active phase and having afirst density, providing at least one second plate consistingessentially of a magnetocalorically active phase and having a seconddensity, the first density of the first plate being greater than thesecond density of the second plate, arranging the first plate and thesecond plate in a stack.
 54. The method according to claim 53, whereinthe first plate and the second plate are arranged so that they are inphysical contact with one another.
 55. The method according to claim 53,wherein the first plate has a first porosity and the second plate has asecond porosity, the second porosity being greater than the firstporosity.
 56. The method according to claim 53, wherein the providing ofthe at least one first plate comprises compacting particles of amagnetocalorically active phase or particles of a precursor of amagnetocalorically active phase.
 57. The method according to claim 56,wherein the providing of the at least one second plate comprisescompacting particles of a magnetocalorically active phase or particlesof a precursor of a magnetocalorically active phase.
 58. The methodaccording to claim 57, wherein the compacting is conducted so as toproduce a lower porosity in the first plate than in the second plate.59. The method according to claim 58, wherein the providing of at leastone first plate and the providing of at least one second plate comprisesproviding a plurality of first plates and a plurality of second plateswhich are interleaved with one another in a stacking direction of thearticle.
 60. The method according to claim 39, further comprising addingone or more of a lubricant, an organic binder or a dispersant to theassembled magnetocalorically active phase or the magnetocaloricallypassive phase or both.
 61. The method according to claim 39, furthercomprising heating the article during the compacting.
 62. The methodaccording to claim 61, wherein the heating forms a magnetocaloricallyactive phase from the precursor.
 63. The method according to claim 39,further comprising applying an outer protective coating to the article.64. The method according to claim 63, wherein applying the outerprotective coating comprises dipping, spraying or electro-deposition.65. A climate control device comprising the heat exchanger according toclaim
 36. 66. An air conditioning system comprising the climate controldevice according to claim 65.